Method of manufacturing incandescent lamps having a transport gas filling



Dec. 16. 1969 R. A. J. M. MEIJER ETAL 3,484,146

METHOD OF MANUFACTURING INCANDESCENT LAMPS HAVING A TRANSPORT GAS FILLING Filed Oct. 1967 INVENTORY AGENT nited States Patent US. Cl. 316- 6 Claims ABSTRACT OF THE DISCLOSURE A method of manufacturing incandescent lamps having a tungsten filament in which during the final stage of manufacture the lamp is evacuated and filled with a mixture of an inert gas and bromine-chlorine hydrocarbons.

The invention relates to a method of manufacturing an incandescent lamp having a filament of tungsten and a bromine-containing transport gas in which during the last manufacturing steps the lamp is evacuated, is then connected to a storage cylinder which contains an inert gas and a bromine-hydrocardon compound, is then filled with the gas mixture to the desired pressure and subsequently closed, usually by sealing an exhaust tube which up to that instant formed one assembly with the bulb.

The bulbs of incandescent lamps obtained in this man ner remain bright till the end of the lifetime of the tungsten coil provided it is ensured that the wall of the bulb during operation of the lamp everywhere reaches a temperature at which the tungsten-bromine compounds formed in the lamp cannot condense. After some time in operation there prveails a dynamic equilibrium in the lamp in which as a result of thermal decomposition of the tungsten compound in the proximity .of the coil the amounts of deposited tungsten and evaporated tungsten are the same.

Suitable bromine-hydrocarbons are, for example, tribromomethane (CHBra), monobramomethane (CH Br) but in particular the dibromomethane (CH Br Other bromine-hydrocarbon compounds also, if required together with a suitable amount of hydrogen, may be used.

Dibromomethane, which is preferably used has a rather low vapour pressure at room temperature. This is a drawback in this particular way of lamp manufacturing. At C. this pressure is only approximately 40 torr.

For practical reasons the partial pressure of the dibromomethane in the storage cylinders may not be equal to said vapour pressure. In fact, it should be prevented that as a result of a decrease in temperature condensation of the dibromomethane occurs in the storage cylinders. A decrease in temperature may occur, for example, at night or during the week-end. Condensation results in unfavourable variation of the composition of the gas mixture in the storage cylinder. After an increase in temperature it takes ample time until a homogeneous gas mixture is present again in a cylinder in which condensation has occurred. For that reason the storage cylinders are normally filled with dibromomethane to a partial pressure of approximately 28 torr which corresponds to the pressure of said compound at approximately 16 C.

In practice this means, that, taking losses into account, for example approximately 10,000 lamps with a volume of approximately 0.25 cm. can be filled to a pressure of approximately 5 atmospheres from a cylinder having a capacity of 8 ltrs. which is filled with a gas mixture of krypton and dibromomethane to a pressure of 8.2 atmospheres.

In this case the storage cylinder may be used until the pressure therein has decreased to approximately 1.2 atmospheres. The cylinder is then emptied, so many litres of krypton of 1.2 atmospheres being lost as the water capacity of the cylinder is. It is not possible to replenish a cylinder in which a pressure of 1.2 atmospheres prevails within a reasonable time with a mixture of krypton and CH Br because the vapour pressure .of the latter is too low for that purpose. The operation of filling the lamps must thus be interrupted for exchanging the storage cylinders in this example after every approximately 10,000 lamps.

It is the object of the invention to mitigate these drawbacks and a particular object of the invention is to enable the filling of more lamps using one storage cylinder, to restrict the loss of rare gas, and to reduce the number of times a new gas mixture has to be prepared and stored in storage cylinders.

According to the invention this may be achieved by using a gas mixture in which bromine and chlorine are present in the form of hydrocarbon compounds.

The greatest improvement is reached if bromochloromethane (CH BrCl) is used. In comparable circumstances the admissible partial pressure of this compound in the storage cylinders is approximately torr. This means that with one storage cylinder filled with bromochloromethane to said pressure, if also the partial pressure of the inert gas is adapted accordingly, approximately three times as many lamps can be filled with the same halogen percentage as is possible with bromomethane in the manner described.

In this manner the loss of rare gas decreases to approximately /3 While the labour time for exchanging filling and the like can be reduced to However, a considerable saving is also obtained already if the gas mixture contains both dibromomethane and dichloromethane to the same partial pressure. From one storage cylinder approximately two times as many lamps can now be filled, while the labour time for certain parts of the manufacturing process can approximately be halved, too.

The invention is based on the use of the property that the mixed bromine-chlorine hydrocarbon compounds and the chlorine hydrocarbon compuonds generally have a higher volatility than the corresponding bromine hydrocarbon compounds.

It was found that in lamps which contain a bromine containing transport gas, for example, half of the bromine may be replaced by chlorine; with this composition in which the ratio bromine-chlorine is 1:1 additional advantages are obtained. The ratio hydrogen to halogen preferably is likewise 1:1 in gramatoms.

It was found that when using such a ratio the total quantity of halogen (bromine together with chlorine) in gramatoms in the lamps may be smaller than in the case of bromine alone, with an equal lifetime and luminous efiiciency of the lamps.

Of course, the method according to the invention is not restricted to the use of bromine-chlorine methane (CH clBr) or mixtures of CH Br and CH Cl For example, also mixtures of CHBr and CHCl may be used, if required by adding hydrogen to the ga mixture. Mixtures of CHBr Cl and CHBrCl or higher hydrohalogenic compounds or higher mixed halogen hydrocarbon compounds may also be used.

The invention will now be described in greater detail with reference to the ensuing specific examples in which reference is made to the accompanying drawing the FIG- URE 1 of which diagrammatically shows the filling (with transport gas) of the lamps according to the invention and FIGURE 2 shows a filling cock.

FIGURE 1 diagrammatically shows a device for filling incandescent lamps with gas. The device comprises in principle a storage cylinder 1 and pipes 2, 6 and 7. In the pipe 2 a reduction valve 3 and a filling cock 4 are arranged. The pipe 2 communicates with a pipe 6 through a three-way valve 5 which pipe 6 serves for transporting the filling gas to the incandescent lamps to be filled and a pipe 7 which is connected to a vacuum pump which is not shown and which serves for evacuating the system. In a practical example the pressure in the storage cylinder 1 having a capacity of 8 litres initially was 24.6 atmospheres. The gas mixture consisted of krypton and 0.45% by volume of CH BrCl. By means of the reduction valve 3 it is ensured that the pressure between the reduction valve and the filling cock 4 remains constantly 1.2 atmospheres a long as the pressure in the storage cylinder has not fallen to said pressure. FIGURE 2 diagrammatically shows a cross-section of a filling cock 4. The filling cock consists in principle of a spindle 8 in which a hollow space 9, capacity 2 cm. is present the spindle being rotatable in a eating 8a provided with two apertures 10 and 11 which communicate with the pipes 2. The filling cock further comprises a pipe 12 which communicates with a vacuum pump. As a result of this the spindle 8 cannot be released from the seating 8a during filling.

By means of this cock 4 a closed quantity of filling gas can be introduced in the rest of the system. During filling the incandescent lamp the procedure is as follows (see also FIGURE 2). The exhaust tube 13 of the incandescent lamp 16 is made to communicate with the pipe 6. The filling system from the filling cock 4 up to and including the incandescent lamp are evacuated until the pressure is approximately 10 torr. The pipe 7 is then closed by means of the three-way cock 5. The filling cock 4 is now rotated so that the space 9 communicates with the evacuated part of the system. Since the lamp 16 (capacity aproximately 0.25 cm?) is to be filled to a pressure of approximately 5 atmospheres at room temperature, said lamp is placed in a vessel containing liquid air 14. After a few seconds the exhaust tube is sealed immediately over the surface of the liquid air 14 in the vessel 15 by means of a gas flame (not shown).

The lamp is now ready for use. 30,000 lamps can be filled from one storage cylinder, taking the losses into account. At a pressure of 8.2 atmospheres in the cylinder, as is maximally possible when using CH Br this number is approximately 10,000 lamps.

It has been found that in incandescent lamps having a gas filling of approximately 1 atmosphere consisting of a gas mixture of, for example, argon and CH Br or CH BrCl the CH Br may be replaced by a smaller quantity of CHgBICl.

In a practical example, a photolamp of 1000 watts at 225 volts with a colour temperature of 3400 K. the gas filling consisting of 700 torr Ar plus 8% by volume of N plus 1% by volume of CH Br may be replaced by 700 torr Ar plus 8% by volume of N plus 0.5% by volume of CH BrCl. A lower partial halogen pressure built up from chlorine and bromine in the ratio 1:1 thus is sufiicient to maintain the cycle while the luminous efficiency of the lamp of approximately 32 1m./W. and the lifetime of approximately hours are at least maintained.

Another advantage of the method according to the invention is that certain types of'lamps can only be manufactured as a result of this method.

So far it was not possible to manufacture long cylindrical high loaded lamps for operation in a vertical position with a bromineor iodine-containing filling gas and a high rare gas pressure. In this type of lamp gas separation occurred as a result of which the iodine or bromine concentration in the upper and lower part of the lamps differed strongly after burning for some time. This had for its result that the lamp began to blacken at one of its filament ends by a local deficiency of halogen while the other end of the filament was strongly attacked by an excess of atomic halogen. As a result of this lamps were obtained having one black end and a comparatively short lifetime.

It has now been found that in such lamps the tungsten halogen cycle can be maintained by chlorine and bromine together without blackening of the bulb and attack of the filament occurring. The good operation of the lamp burning in a vertical position is ensured in spite of the demixing of the gas filling of the lamp. However, the demixing is such that the tungsten-halogen cycle on one side of the lamp mainly occurs between tungsten and bromine and on the other side of the lamp space mainly between tungsten and chlorine.

In the centre of the lamp both cycles occur.

What is claimed is:

1. A method of manufacturing incandescent lamps having tungsten filaments and a bromine-containing transport gas, in which during the last manufacturing steps the lamp is evacuated, then filled with a mixture of an inert gas and bromine in the form of a bromine-hydrocarbon compound from a storage cylinder and is then sealed, characterized in that a gas mixture is used in which bromine and chlorine are present in the form of hydrocarbon compounds.

2. A method as claimed in claim 1, characterized in that a gas mixture is used which contains an inert gas and a hydrocarbon compound which contains both chlorine and bromine.

3. A method as claimed in claim 1, characterized in that a gas mixture is used which contains an inert gas, a bromine-hydrocarbon compound and a chlorine-hydrocarbon compound.

4. A method as claimed in claim 1, characterized in that a gas mixture is used in which the ratio bromine to chlorine in gramatoms is approximately 1:1 and the ratio hydrogen to halogen likewise 1:1.

5. A method as claimed in claim 1, characterized in that a gas mixture is used in which bromochloromethane is present.

6. A method as claimed in claim 1, characterized in that a gas mixture is used in which dibromomethane and dichloromethane are present in a ratio of 1:1 in grammolecules.

References Cited UNITED STATES PATENTS 3,194,625 7/1965 Danko 3l6--20 2,596,469 5/1952 Cooper 31620 1,789,556 1/1931 Machlett 316-20 JOHN F. CAMPBELL, Primary Examiner R. J. CRAIG, Assistant Examiner U.S. Cl. X.R. 3l617, 24, 30 

